1. Technical Field of the Invention
The present invention relates to solid photoprotective compositions comprising, formulated into a physiologically acceptable medium:                a) at least one fatty phase,        b) at least one organic UV-screening agent,        c) at least a fraction of metal oxide-based mineral nanopigments, and        d) at least one octenylsuccinic anhydride-esterified starch salt.        
The present invention also relates to the use of at least one octenylsuccinic anhydride-esterified starch salt in a solid photoprotective composition comprising at least one fatty phase, at least one organic UV-screening agent and at least a fraction of metal oxide-based mineral nanopigments, with the aim of increasing the sun protection factor.
2. Description of Background and/or Related and/or Prior Art
It is well known that light radiation with wavelengths of between 280 nm and 400 nm permits tanning of the human epidermis and that light rays with wavelengths of between 280 and 320 nm, which are known as UV-B, cause skin burns and erythema that may be harmful to the development of a natural tan; this UV-B radiation should thus be screened out.
It is also known that UV-A rays with wavelengths of between 320 and 400 nm, which cause tanning of the skin, are liable to effect impairment therein, especially in the case of sensitive skin or of skin that is continually exposed to sunlight. UV-A rays in particular cause a loss of elasticity of the skin and the appearance of wrinkles, leading to premature aging. They promote triggering of the erythemal reaction or amplify this reaction in the case of certain individuals and may even be the cause of phototoxic or photoallergic reactions. It is thus desirable also to screen our UV-A radiation.
Many cosmetic compositions for photoprotecting the skin are known to this art.
They generally contain, in varying concentrations, one or more standard liposoluble organic screening agents and/or standard water-soluble organic screening agents capable of selectively absorbing the harmful UV rays, these screening agents (and the amounts thereof) being selected as a function of the desired sun protection factor, the sun protection factor (SPF) being expressed mathematically by the ratio of the dose of UV radiation required to reach the erythema-forming threshold with the UV-screening agent to the dose of UV radiation required to reach the erythema-forming threshold without UV-screening agent.
To provide antisun/sunscreen compositions with high sun protection factors in order to render same more effective and to reduce the contents of organic UV-screening agents for reasons of skin tolerance, it is common practice to include screening systems containing organic UV-screening agents combined with mineral agents for screening out UV radiation, such as nanopigments of metal oxide (TiO2 or ZnO)
The formulation forms most commonly used for antisun products are emulsions. Mention may be made firstly of direct emulsions of oil-in-water type (i.e., a cosmetically and/or dermatologically acceptable support comprising an aqueous dispersing continuous phase and a fatty dispersed discontinuous phase) or inverse emulsions of the water-in-oil type (aqueous phase dispersed in a continuous fatty phase), which contains, in varying concentrations, one or more standard liposoluble organic screening agents and/or standard water-soluble organic screening agents. In such emulsions, the hydrophilic screening agents are present in the aqueous phase and the lipophilic screening agents are present in the fatty phase. In such emulsions, the metal oxide nanopigments, depending on their hydrophilic or hydrophobic nature, are dispersed in the aqueous or oily phase.
These emulsions are generally in the form of creams, lotions or milks. They are difficult to spread and to deposit on the lips or on certain sensitive areas of the face such as the contour of the eyes, the nose, the cheekbones or scars due to the fact that the product may run onto the area to be protected at the time of use.
To solve this problem, numerous products in solid form are known in the cosmetics industry in the field of care of the lips or of these sensitive areas of the face. Mention may especially be made, in the field of lipcare, of lip-repairing pencils, antisun sticks and moisturizing sticks. Specifically, it is particularly advantageous to have products in solid form, since such products are very practical to use and easy to transport. They allow good spreading and good deposition on the lips or other areas of the face.
The current sticks for photoprotecting the lips and the face contain as antisun/sunscreen emulsions screening systems containing both organic UV-screening agents and mineral screening agents.
There is an ever-increasing need to obtain in this type of support high sun protection factors without increasing the content of UV-screening agents present in the composition, for reasons of skin tolerance.